(corrected- thanks lazygun, I had initially thought it was the ff ligature)
At least one of the fonts used in the game changes occurrences of "ffi" to a ligature, but the font used doesn't have an appropriate symbol so it shows as a black box. This can be seen in the description of the planetary arcology structure and in interplayer messaging.
This was reported fixed in Alpha 4, so it may be a regression.
To be precise, it's the "ffi" ligature that causes problems.
Fixed and deployed. At the time of the original fix there was no standard way to disable ligatures, so I fixed it using non-standard CSS. After the standard developed, the non-standard CSS was discontinued.
This bug is back in all(?) display fonts - show up in player messaging and planet improvement description.
If this detracts too much time away from fixing other bugs/implementing new features I think it's not so much a priority issue. We can always type "ff i" instead of "ffi". If it's just a simple fix or font change then that's excellent.
Fixed in messaging. I couldn't reproduce the problem in planet improvements. If this still happens, please re-open with screenshot.