Shiny Charizard

Legendary Skial King
So I was reading the wiki...

After downgrading a building, it will still gain health when upgrading it again; for example, when downgrading a level 3 Sentry to level 1, it will keep the 216 HP from the level 3 state and will keep gaining max HP when upgrading it again.
  • Attaching a regular Sapper on a Sentry Gun affected by this glitch will result in a server crash.
 
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Product Update - Valve​
An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include:

  • Fix server crash bug caused by setting tf_mm_servermode before map command
  • Increased The Red Tape Recorder's downgrade speed from 1.6 seconds to 3.0 seconds.
  • Fixed The Huo Long Heatmaker not consuming additional ammo while firing
  • Fixed building health compounding after being downgraded
  • Fixed direction arrow showing on teleporter exits
  • Cleaver is now available in Medieval mode
  • Fixed missing Lollichop taunt sound
  • Fixed item conflicts with The Champ Stamp
  • Fixed item conflicts with The Triad Trinket
 
Team Fortress 2 Update Released


Product Update - Valve

An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include:


  • Fix server crash bug caused by setting tf_mm_servermode before map command
  • Increased The Red Tape Recorder's downgrade speed from 1.6 seconds to 3.0 seconds.
  • Fixed The Huo Long Heatmaker not consuming additional ammo while firing
  • Fixed building health compounding after being downgraded
  • Fixed direction arrow showing on teleporter exits
  • Cleaver is now available in Medieval mode
  • Fixed missing Lollichop taunt sound
  • Fixed item conflicts with The Champ Stamp
  • Fixed item conflicts with The Triad Trinket

that has nothing to do with the crash