Performance issues, resulting in under 30fps on what would be considered otherwise 'decent' systems that meet the mimum specifications. i.e: Intel Core2 Duo, AMD Athlon64 x2, or better, 2 GB RAM, NVidia Geforce 8600GT, ATI Radeon 3670HD or equivalent ~0.5Ghz core <1Gb ram video card. Reported many, many times, see sample
In certain cases Miasamata won't start properly or crashes while starting
Changing game resolution adversely affects performance and water quality (see 'grainy water') or causes issues with text and menus.
If you look at your journal then switch immediately to the map and zoom in with right-mouse, (possibly switching more than once) and then cancel, your view is locked and does not respond to the mouse. Just re-open and then close the first thing you opened to get control back.
Also reported when you close the map before it has finished opening
The Creature sometimes won't go away, runs back and forth or in loops and never leaves, even though you are hidden. Take your chances and do a runner or sneak off while he isn't looking.
If you jump while standing right next to something (e.g.: a ledge or a rock) instead of jumping up on it, you will be thrown backwards. Take a few steps back and take a run at it and jump a bit earlier
If you research a plant, or find a duplicate of a note, the journal opens, but nothing else happens.
It will be moved to the end of the research or notes section and be read again there. 
A number of the ingredients 'fall through' the storage trays, especially the grey fungus and spadix plant, leaving a tiny sliver of the plant visible in the tray. If you crouch down, you can see most of the plant hanging under the table...
The game will 'stall' or 'stutter' as it loads the music when entering a campsite
Although practically everything else in the game updates 'in real time' the watch hands do not. If you need to check the passage of time, keep putting your watch away and pull it out regularly.
Sometimes there is a green static-like rectangle around the (animated sprite?) flame on the lighter