Depending on how you soldered them in, not necessarily. I need to get some better measurements made [under a microscope], but the physical difference between a chattering switch and a clean one is as little as 0.01mm, +/- 0.00025mm.
If this theory is right, this problem cannot be seen in linear switches; it will only present on tactiles, and even then, only on some tactiles. The tolerences here are small enough that hamfisted soldering could introduce it - or just pressure at the right angle on the leg of the stationary contact. But it can - and does - present these symptoms on never-soldered switches...
I gave Zeal a heads-up with the core details already, but I need some better measurements before I'm comfortable posting everything. I'm hoping to have a full write-up late this weekend.
(Also, hi, finally got off my arse and registered an account instead of lurking.)