Incremental compilation of opaque type fail

[soronpo]

Clean complete compilation works, but if we leave a single-line commented, compile and then uncomment it, then we get the error.

Compiler version

v3.1.0-RC1

Minimized code

Minimized project available at: https://github.com/soronpo/dottybug/tree/inc_comp_opaque_error

MyOpaque.scala

trait Container[T]
opaque type MyOpaque[W <: Int] = Int
extension [W <: Int](myOpaque: MyOpaque[W]) def getContainer: Container[W] = ???

Test.scala

val myOpaque: MyOpaque[8] = ???
val container = myOpaque.getContainer
//after successful compilation, uncomment the following line to get the error
//val shouldWork = summon[container.type <:< Container[8]]

Output

[error] 4 |val shouldWork = summon[container.type <:< Container[8]]
[error]   |                                                        ^
[error]   |  Cannot prove that (container : Container[Int]) <:< Container[(8 : Int)].
[error] one error found

Expectation

No error in incremental compilation.

[griggt]

Also fails separate compilation with all code uncommented.