Im having this issue as well. it seems as if you wait for like 15 seconds after you DL the app, you can press the button fine, and cydia will still function fine.
edit: Did a few googles and found stuff:
1. You can try rebooting your phone, this seems to fix the issue for a bit, then it comes back.
2. reinstall cydia. (this by far has worked for everyone using it..but theres always that ONE)
3. restore/rejb. Last resort.. I would just say stick it out..wtf ever. dont be a whiny cry baby about a restore.. if your complaining then be prepared. its called syncing.
This started happening to me after I passed out with cydia still running, and insomnia on.. so my phone just stayed on for like 13 hours.. 3% battery left when I woke up, and cydia was randomly crashing.. Too much use maybe..