PowerShell.OnIdle seems not to fire in PSReadline 2.0 beta (repro)

[csr-nick]

Environment data

PS version: 5.1.17134.228
PSReadline version: 2.0.0-beta3
os: 10.0.17134.1 (WinBuild.160101.0800)
PS file version: 10.0.17134.1 (WinBuild.160101.0800)

Steps to reproduce or exception report

Further to #773, I think I can repro this pretty reliably now. It seems that the OnIdle event isn't fired when another event subscriber already exists.

PS> powershell -noprofile
PS> Register-EngineEvent -SourceIdentifier PowerShell.OnIdle -Action {Write-Host '*idle*'} -MaxTriggerCount 1
PS> *idle*
PS> $timer = New-Object System.Timers.Timer -Property @{ Interval = 1000; AutoReset = $false }
PS> Register-ObjectEvent $timer Elapsed -Action { Write-Host '*timer*' } -MaxTriggerCount 1
PS> Register-EngineEvent -SourceIdentifier PowerShell.OnIdle -Action {Write-Host '*idle*'} -MaxTriggerCount 1
PS> # nothing...
PS> Get-EventSubscriber

SubscriptionId   : 3
SourceObject     : System.Timers.Timer
EventName        : Elapsed
SourceIdentifier : 6ac2a48b-3498-47af-b32b-f82652dda9f5
Action           : System.Management.Automation.PSEventJob
HandlerDelegate  :
SupportEvent     : False
ForwardEvent     : False

SubscriptionId   : 4
SourceObject     :
EventName        :
SourceIdentifier : PowerShell.OnIdle
Action           : System.Management.Automation.PSEventJob
HandlerDelegate  :
SupportEvent     : False
ForwardEvent     : False

PS> Remove-Module PSReadline
PS> *idle*

[nickcox]

Not sure if it's relevant but this also seems to affect PSReadLine on pwsh.

PS version: 6.1.3
PSReadline version: 2.0.0-beta3
os: 10.0.17134.1 (WinBuild.160101.0800)
PS file version: 6.1.3

[musm]

any progress on this bug?

[musm]

thanks, hopefully this can be pushed to a beta release soon