This is a collection of various issues I've come across over the past couple months:
Site Credits calculation
I discovered through trial and error that Credits appear to be awarded at a maximum of five per category (upload/comment/favourite) per day, likely as an anti-spam measure so newbies can't Morbius sweep all the perks in one go. Over the past two days, however, I've noticed incongruities in my own history that leave me questioning how the throttle actually works.
This is my credits history for the past four days. Note the transactions highlighted in red: these are my last five uploads yesterday (April 24). These three earlier uploads received no credits. Now examine the transactions highlighted in green: these were the uploads from the day before. Note the time stamps: 6:28, 6:32, 6:36, 6:39, and 6:54 PM GMT.
The transactions in red are dated 6:32, 6:34, 6:41, 6:47, and 7:42 PM GMT; the first three that weren't calculated were posted at 5:02, 6:20, and 6:26. I think I know what's going on: I had assumed that the throttle reset along with the site clock (see the Featured Artist widget, which updates at 12 AM GMT). Instead, it seems the counter lasts for 24 hours from the time the credits are awarded: the first three uploads on the 24th were thus made during the cooldown period and so didn't earn Credits, whereas by complete luck I managed to perfectly stagger the later uploads so they didn't overlap with Sunday's posts:
6:28
→ 6:32
6:32
→ 6:34
6:36
→ 6:41
6:39
→ 6:47
6:54
→ 7:42
At the risk of starting an argument about gamification, I'll admit that once I figured out there was a cap, I started strategizing to maximize my returns. As it works now, "optimal" behaviour means progressively delaying interactions later each day, until you're redlining before bed and have to skip a day entirely. I would suggest syncing the Credits cooldown to the server clock to normalize the interval, thereby rewarding Credits reliably.
Invisible titles
You may have noticed in the credits report, 'Favorited "".' This is an issue I'd noticed some time ago: users that have not supplied a name, and submissions that are not given a title, will render blank in several UI elements, e.g. clickable links. Interestingly, submissions with blank titles will default to "untitled" in plain text; a failsafe can probably be coded, similar to the tooltips on submission thumbnails falling back to the user's @ handle if no name is given.
Standardizing syntax
There have been longstanding discrepancies in how the post preview actually translates to the published text; this is probably due to the site juggling three different markups: HTML, BBCode, and Markdown, in three separate places: submission comments, forum posts, and text submissions. Harmonizing them all will undoubtedly take work and/or custom rigging (and special consideration to Literature will receive its own section in Site Suggestions), but it will hopefully clarify what works where and weed out little glitches like line breaks.
The Unfavouritables
So, rather than, y'know, ask the siterunner, a couple months back I went on a manual crawl of the Archives in a bid to track down the exact date Side 7 became an art gallery. (Mad kudos to BK for coding infinite scroll in a way that doesn't crash the browser after ten minutes, cough cough dA—for the record, I made it to Summer '02 before memory leakage elsewhere forced a reboot.)
In the process, I found several pieces that no matter how I tried, I couldn't favourite—originally I thought this was down to them being ancient and related to the since-fixed glitch for descriptions displaying out of bounds, but as recently as Friday it's still cropping up.
Comments v. Replies
This one's caught me out many times: When replying to multiple comments on a submission/journal, only the first reply nests correctly; subsequent replies will post as standalone comments. To respond properly, you must navigate off the page and reload it for each individual reply—F5 Refresh does not work.
Directly related to this is a feature request: editable gallery comments. Currently the closest we have is the submission owner being able to delete comments, which while okay for one's own goofs, doesn't help users responding to you. DeviantArt has a 24-hour grace period in which a comment can be revised, plus it keeps a publicly-available record of all edits made during then, so if keeping a paper trail is a concern there is a working proof-of-concept.
GIF problems
Several users are having problems uploading GIFs: the thumbnails work but the main image fails.
More to follow when I've remembered I've forgotten them. :x