I can run the following command in bash without any errors:

$ find /d/Code/Web/Development/Source/ \( -name '*.cs' -o -name '*.cshtml' \) -exec grep -IH UserProfileModel {} \;

I wrote a function in .bash_aliases to quickly run this command:

search() {
    local file_type file_types find_cmd opt OPTARG OPTIND or pattern usage

    usage="Usage: search [OPTION] ... PATTERN [FILE] ...
Search for PATTERN in each FILE.
Example: search -t c -t h 'hello world' /code/internal/dev/ /code/public/dev/

Output control:
  -t    limit results to files of type"

    if [[ $1 == --help ]]; then
        echo "$usage"
        return
    fi

    file_types=()
    while getopts ":t:" opt; do
        case $opt in
            t)
                file_types+=("$OPTARG")
                ;;
            ?)
                echo "$usage"
                return
                ;;
        esac
    done
    shift $((OPTIND-1))

    if (( $# == 0 )); then
        echo "$usage"
        return
    fi

    pattern=$1
    shift

    if (( $# == 0 )); then
        echo "$usage"
        return
    fi

    find_cmd=(find "$@" '\(')
    or=""
    for file_type in "${file_types[@]}"; do
        find_cmd+=($or -name \'*.$file_type\')
        or="-o"
    done
    find_cmd+=('\)' -exec grep -IH "$pattern" {} '\;')

    "${find_cmd[@]}"
}

However, the function throws an error:

find: paths must precede expression

If I change the last line to echo "${find_cmd[@]}", it prints the exact same command as above:

$ search -t cs -t cshtml UserProfileModel /d/Code/Web/Development/Source/
find /d/Code/Web/Development/Source/ \( -name '*.cs' -o -name '*.cshtml' \) -exec grep -IH UserProfileModel {} \;

I don't understand why it would work when run in the console but fail when run inside a function.

Also, if I simplify the function to just the command it works:

search() {
    find /d/Code/Web/Development/Source/ \( -name '*.cs' -o -name '*.cshtml' \) -exec grep -IH UserProfileModel {} \;
}

I am editing .bash_aliases in Notepad++, but I have made sure the line endings are Unix format.

Edit

Per F. Hauri's advice below, I enabled debugging. Apparently this is the command that's actually being executed:

find /d/Code/Web/Development/Source/ '\(' -name ''\''*.cs'\''' -o -name ''\''*.cshtml'\''' '\)' -exec grep -IH UserProfileModel '{}' '\;'

I'm not sure what to make of this information. Removing the escape character before the parens cause it to throw a different error:

find: missing argument to -exec