Colon as a delimiter transforms numbers wrong

[E_Langlet]

Hi!

I am trying to combine two fields into one field with colon as delimiter. 

The fields have the following values:

field1 :1013988
field1:76

When I run the following script,"field1" &':'& "field2" as "Combinedfield", I get 1013989:16 as output, which is obviously wrong. Does anybody have any idea why I get the wrong numbers? The data is more than 100 000 rows and this error only occurs for some rows. The datasource is SAP.

If I instead run the following codes I get correct outputs:

"field1" &'-'& "field2" as "Combinedfield"

output: 1013988-76

or 

text("field1" &':'& "field2") as "Combinedfield", 

output:1013988:76

Can anyone explain why it gets wrong and why it only gets wrong in some cases? How does 76 turn into 16 and how does the final 8 turn into 9?

[Or]

At a guess, looks like it's being parsed as a time, and 76 is getting converted into an extra minute or hour, leaving 16 seconds or minutes behind.